Bone fixation assembly

ABSTRACT

A bone fixation assembly and associated method. The bone fixation assembly includes a bone fastener having a head and a bone-engaging portion, a receiver defining an opening along a first axis for receiving the bone fastener at a variable angle, and at least one supporting augment coupled to the bone fastener. The receiver has an inner articulation surface at a lower portion of the opening and matingly articulates with the supporting augment.

Various internal fixation devices are known for correcting and/orstabilizing malformation or other condition of bones, including longbones and the spine. Such fixation devices can include elongated rodsaffixed with bone screws at desired orientations relative to the bone orspine. Some known bone fixation devices utilize poly-axial ormulti-axial screws for adjusting the fixation device at a desiredorientation.

Although the existing fixation devices can be satisfactory for theirintended purposes, there is still a need for modular bone screwassemblies that can provide variable angle orientation, and which areeasy to assemble.

SUMMARY

The present teachings provide a bone fixation assembly. The bonefixation assembly includes a bone fastener having a head and abone-engaging portion, a receiver defining an opening along a first axisfor receiving the bone fastener at a variable angle, and at least onesupporting augment coupled to the bone fastener. The receiver has aninner articulation surface at a lower portion of the opening andmatingly articulates with the supporting augment.

The present teachings also provide a method for bone fixation. Themethod includes providing a receiver defining an opening along a firstaxis for receiving a bone fastener at a variable angle, inserting thehead of the bone fastener into the opening, and inserting at least onesupporting augment into the opening. The at least one supporting augmentis articulable with an inner articulation surface of the receiver. Themethod further includes coupling the at least one supporting augment tothe head of the bone fastener, and varying the angle of the bonefastener relative to the first axis by articulating the at least onesupporting augment relative to the articulation surface.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples areintended for purposes of illustration only and are not intended to limitthe scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a side view of a bone fixation assembly according to thepresent teachings shown with an elongated fixation member;

FIG. 1A is a side view of a bone fixation assembly according to thepresent teachings similar to FIG. 1, illustrating a variable angleorientation;

FIG. 2 is a sectional view of the bone fixation assembly of FIG. 1 takenalong the axis 2—2 of FIG. 1;

FIG. 3 is an enlarged view of detail A of FIG. 2 shown additionally inexploded view;

FIG. 4 is an enlarged perspective view of a receiver of the bonefixation assembly of FIG. 3;

FIG. 5 is an enlarged perspective view of a bone fastener of the bonefixation assembly of FIG. 3;

FIG. 6 is an enlarged perspective view of a supporting augment of thebone fixation assembly of FIG. 3;

FIG. 7 is an enlarged perspective view of a cap ring of the bonefixation assembly of FIG. 3;

FIG. 8 is an enlarged perspective view of a cap of the bone fixationassembly of FIG. 3;

FIG. 9 is an enlarged perspective view of a fastener ring of the bonefixation assembly of FIG. 3; and

FIG. 10 is an end view of the bone fixation device of FIG. 2.

DESCRIPTION OF VARIOUS ASPECTS

The following description is merely exemplary in nature and is in no wayintended to limit the invention, its application, or uses.

Referring to FIGS. 1, 1A, and 2, an exemplary variable angle bonefixation assembly 100 is illustrated according to the present teachings.The bone fixation assembly 100 can include a receiver 102 defining anopening 118 along a first axis “X”, and a bone fastener 104. The bonefastener 104 can be assembled on the receiver 102 for variable angleangulation relative to the first axis X on an angulation cone of angleα, as illustrated in FIG. 1A. The bone fastener 104 can include a head108 and a bone-engaging portion 106, which can be shaped as a screw orother anchor, as shown in FIG. 5. The bone-engaging portion 106 caninclude, for example, a plurality of threads 107 and an anchoring tip109. The head 108 can include a circumferential exterior groove 111 forengaging a retention member, such as a fastener ring 112, shown in FIG.9, as discussed below.

Referring to FIGS. 3-10, the receiver 102 can include two substantiallyparallel arms 126 extending in a direction away from the fastener 104.The arms define a channel 128 along a second axis “Y” generallyperpendicular to the first axis X. The channel 128 can be shaped toreceive an elongated fixation member 130, such as, for example, a spinalfixation rod or other fixation bar, as shown in FIG. 1. The interiorsurface of the arms 126 can include a thread pattern or otherinterlocking form 132, such as a helically-wound interlocking formsimilar to the one disclosed and described in U.S. Pat. No. 6,726,689,filed Sep. 2, 2002, the disclosure of which is incorporated herein byreference. It will be appreciated that other thread forms can also beused. The interlocking form 132 can mate with a closure member (notshown) having a corresponding interlocking form for securing thefixation member 130 in the receiver 102 such that radial splaying of thearms 126 can be operatively resisted.

Referring to FIGS. 3-6, the receiver 102 can include an articulationsurface 120 at a lower portion of the opening 118 and adjacent a lowerend 122 thereof. The articulation surface 120 can articulate with acorresponding curved exterior surface 124 of one or more discretesupporting augments 110. The conforming articulating surfaces 120, 124can be portions of generally spherically surfaces or other surfaces thatcan provide desired variable angle fixation. Each supporting augment 110can include a curved interior surface 125 which can be shaped to conformto at least a portion of the head 108 of the bone fastener 104.Referring to FIG. 6, in one aspect, each supporting augment 110 caninclude upper and lower substantially planar surfaces 143 a, 143 b,first and second oppositely inclined substantially planar end surfaces140 a, 140 b, and an upper curved cutout or notch 136 adjacent to firstend surface 140 a. The upper surface 143 a can define a sharp corner 145b with the second end surface 140 b, and a blunt or rounded corner 145 awith the first end surface 140 a.

The supporting augments 110 can be positioned relative to each othersuch that upon assembly each of the first and second end surfaces 140 a,140 b of one supporting augment 110 can mate with the second and firstend surfaces 140 b, 140 a, respectively, of the other supporting augment110, thereby completing an annular curved surface with a 360-degreecircumference. The shape of the supporting augments 110 can be definedfor ease of assembly and angulation during assembly. For example, duringassembly, the supporting augments 110 can be positioned such that thesharp corner 145 b of each supporting augment 110 rides on the notch 136of the other supporting augment 110, such that the supporting augments110 overlap partially, and the overall size/volume of the resultingconfiguration is smaller during assembly than the size of the assembledsupporting augments 110.

Referring to FIGS. 3, 6 and 9, each supporting augment 110 can alsoinclude a circumferential interior groove 134 shaped for partiallyreceiving the fastener ring 112. The fastener ring 112 can be asubstantially flat and compliant split ring with an outer boundary 113and an inner boundary 115. In assembly, at least a portion of the outerboundary 113 of the fastener ring 112 can be engaged with the interiorgroove 134 of the supporting augment 110. The inner boundary 115 of thefastener ring 112 can engage the exterior groove 111 of the head 108 ofthe bone fastener 104.

Referring to FIGS. 3, 7, and 8, the bone fixation assembly 100 can alsoinclude a cap 116, which can engage an upper portion of the head 108.The cap 116 can include a circumferential exterior cap groove 117 forengaging a cap ring 114. The cap ring 114 can be a compliant split ringand can be positioned in engagement between the cap groove 117 and aninterior groove or slot 119 defined in the receiver 102. Pressing thecap 116 against the head 108 of the bone fastener 104 with the fixationmember 130 can prevent angulation of the bone fastener 104 relative tothe receiver 102, thereby retaining the fastener 104 in a fixedorientation.

The bone fixation assembly 100 can be assembled during or before thesurgical procedure. Generally, the head 108 of the bone fastener 104 canbe inserted first into the opening 118. At least one supporting augment110 can be inserted into the opening 118, and coupled to the head 108 ofthe bone fastener 104. The angle α of the bone fastener 104 relative tothe first axis X can then be varied by articulating the supportingaugment 110 relative to the articulation surface 120.

In one exemplary aspect, the fastener ring 112 can be assembled on theexterior groove 1 11 of the head 108 of the bone fastener 104. The head108 with the fastener ring 1 12 thereon can be inserted into thereceiver 102 through the lower end 122 of the opening 118, and can bepushed above its final seating position to facilitate assembly, asnecessary. The supporting augments 110 can then be inserted from anupper end 123 of the receiver 102 and can be pushed toward the fastenerring 112 while the bone fastener 104 is pulled down, until thesupporting augments 110 engage the fastener ring 112 and the bonefastener 104 is seated in engagement with the receiver 102. In thisposition, the bone fastener 104 can freely angulate relative to axis X,but can not be removed from the receiver 102 either through the lowerend 122 or through the upper end 123. For facilitating insertion thesupporting augments 110 can be arranged with partial overlappingtherebetween, as discussed above. In another aspect, the supportingaugments 110 can be inserted into the receiver 102 through the lower end122 of the opening 118, and manipulated into engagement with thefastener ring 112.

The cap 116 with the cap ring 114 can be inserted from the upper end 123of the receiver 102 such that the cap ring 114 engages the interior slot119 of the receiver 102. For a particular application, such as spinalfixation, a rod or other longitudinal fixation member 130 can bepositioned along the channel 128 and pressed against the cap 116 with acompression member (not shown). Pressing the cap 116 against the head108 with the compression member secures the bone fastener 104 in adesired orientation.

It will be appreciated that the modularity and shape of the variousparts of the bone fixation assembly 100 can provide a compact(non-bulky) bone fixation device, which can be easily assembled duringthe surgical procedure, or can also be at least partially pre-assembled.Furthermore, the bone fixation assembly 100 can be easily configured foraccommodating various surgical situations at the site of operation asdesired by the surgeon.

The fixation assembly can be formed from biocompatible materials, suchas, for example, metallic materials.

The foregoing discussion discloses and describes merely exemplaryarrangements of the present invention. One skilled in the art willreadily recognize from such discussion, and from the accompanyingdrawings and claims, that various changes, modifications and variationscan be made therein without departing from the spirit and scope of theinvention as defined in the following claims.

1. A bone fixation assembly comprising: a bone fastener having a headand a bone-engaging portion; a receiver defining an opening along afirst axis for receiving the bone fastener at a variable angle, thereceiver having an inner articulation surface at a lower portion of theopening; and at least one supporting augment coupled to the bonefastener and matingly articulable with the articulation surface of thereceiver.
 2. The bone fixation assembly of claim 1, wherein the at leastone supporting augment includes two separate supporting augments.
 3. Thebone fixation assembly of claim 1, wherein the articulation surface issubstantially spherical and wherein the supporting augment has an outermating surface that is substantially spherical.
 4. The bone fixationassembly of claim 1, wherein a lower end of the opening is configuredfor receiving the head of the bone fastener therethrough.
 5. The bonefixation assembly of claim 4, further comprising a fastener ring, thefastener ring couplable to the head of the bone fastener such that thefastener ring can be inserted assembled to the bone fastener from thelower end of the opening.
 6. The bone fixation assembly of claim 5,wherein the fastener ring is supportable on a groove of the supportingaugment.
 7. The bone fixation assembly of claim 6, wherein the fastenerring is a split ring.
 8. The bone fixation assembly of claim 6, whereinthe supporting augment is shaped for allowing variable angulation of thefastener.
 9. The bone fixation assembly of claim 2, wherein eachsupporting augment includes a notch on an upper surface of the augment.10. The bone fixation assembly of claim 8, wherein each supportingaugment includes two oppositely inclined end surfaces.
 11. The bonefixation assembly of claim 9, wherein each supporting augment is shapedfor partial overlapping about the notch during assembly.
 12. The bonefixation assembly of claim 8, wherein the supporting augment is furthershaped for preventing removal of the fastener when the ring is coupledto the supporting augment and to the head of the fastener.
 13. The bonefixation assembly of claim 1, further comprising a fastener cap forcoupling the head of the fastener to an inner surface of the receiver.14. The bone fixation assembly of claim 13, further comprising a capring for coupling the fastener cap and the receiver.
 15. The bonefixation assembly of claim 14, wherein the receiver defines a channelextending along a second axis generally perpendicular to the first axis.16. The bone fixation assembly of claim 15, wherein the channel isshaped for receiving a fixation rod above the fastener cap.
 17. The bonefixation assembly of claim 14, wherein the cap ring is a split ring. 18.A method for spinal fixation comprising: providing a receiver definingan opening along a first axis for receiving a bone fastener at avariable angle, the receiver having an inner articulation surface at alower portion of the opening; inserting the head of the bone fastenerinto the opening; inserting at least one supporting augment into theopening, the at least one supporting augment articulable with thearticulation surface; coupling the at least one supporting augment tothe head of the bone fastener; and varying the angle of the bonefastener relative to the first axis by articulating the at least onesupporting augment relative to the articulation surface.
 19. The methodof claim 18, wherein coupling the at least one augment is performedafter inserting the head of the bone fastener into the opening.
 20. Themethod of claim 18, wherein inserting the head of the bone fastener intothe opening includes inserting the head through a lower end of theopening.
 21. The method of claim 20, wherein coupling the at least onesupporting augment to the head of the bone fastener includes preventingthe head of the bone fastener from withdrawal through the opening. 22.The method of claim 18, wherein coupling the at least one supportingaugment to the head of the bone fastener includes coupling a retentionmember to the at least one supporting augment and to the head of thebone fastener.
 23. The method of claim 20, further comprising insertinga cap through an upper end of the opening for engaging the head of thebone fastener.